var sn = [ 42, 41 ], dz = 43, fx = 1, n, ctx = document.getElementById("gameCavas").getContext("2d");  
function draw(t, c) {
    ctx.fillStyle = c;
    ctx.fillRect(t % 20 * 20 + 1, ~~(t / 20) * 20 + 1, 18, 18);
}
document.onkeydown = function (e) {
    fx = sn[1] - sn[0] == (n = [-1, -20, 1, 20][(e || event).keyCode - 37] || fx) ? fx : n
};
!function () {
    sn.unshift(n = sn[0] + fx);
    if (sn.indexOf(n, 1) > 0 || n < 0 || n > 399 || fx == 1 && n % 20 == 0 || fx == -1 && n % 20 == 19)
        return alert("GAME OVER");
    draw(n, "Lime");
    if (n == dz) {
        while (sn.indexOf(dz = ~~(Math.random() * 400)) >= 0);
        draw(dz, "Yellow");
    } else
        draw(sn.pop(), "Black");
    setTimeout(arguments.callee, 130);
}();  